The formation of slime by microorganisms is a problem which attends many systems. For example, lagoons, lakes, ponds, pools, and such systems as cooling water systems and pulp and paper mill systems all possess conditions which are conducive to the growth and reproduction of slime-forming microorganisms. In both once-through and recirculating cooling systems, for example, which employ large quantities of water as a cooling medium, the formation of slime by microorganisms is an extensive and constant problem.
Airborne organisms are readily entrained in the water from cooling towers and find this warm medium an ideal environment for growth and multiplication. Aerobic and heliotropic organisms flourish on the tower proper while other organisms colonize and grow in such areas as the tower sump and the piping and passages of the cooling system. Such slime serves to deteriorate the tower structure in the case of wooden towers. In addition, the deposition of slime on metal surfaces promotes corrosion. Furthermore, slime carried through the cooling system plugs and fouls lines, valves, strainers, etc. and deposits on heat exchange surfaces. In the latter case, the impedance of heat transfer can greatly reduce the efficiency of the cooling system.
In pulp and paper mill systems, slime formed by microorganisms is also frequently and, in fact, commonly encountered. Fouling or plugging by slime also occurs in the case of pulp and paper mill systems. Of greater significance, the slime becomes entrained in the paper produced to cause breakouts on the paper machines with consequent work stoppages and the loss of production time or unsightly blemishes in the final product which results in rejects and wasted output. The previously discussed problems have resulted in the extensive utilization of biocides in cooling water and pulp and paper mill systems. With the advent of pollution controls which prohibit discharge of biocidal materials to receiving streams without pre-treatment for removal or destruction thereof, the water-treatment industry has been exploring various methods and materials in an attempt to reduce slime problems or to enhance the effectiveness of biocidal agents.
In certain instances it is necessary to minimize and fluidize slime formation because of the ultimate effect on the products produced as in the pulp and paper industry. In other applications if the amount of slime formations can be maintained and preferably in a fluidized state, the problems associated therewith are often times minimized to a great degree and sometimes cured by the use of low feed rate biocide treatments. This is particularly the case in industrial cooling water treatment where if slime deposits can be detached or be made to slough off the structures of the cooling water structures and maintained dispersed in the water, operation of the system may be continued with little or no biocide additive.
The slimes generally found in aqueous systems are those which are bacterial and/or fungal in derivation. The primary problem causes which are generally found in water are the aerobacter bacteria and specifically aerobacter aerogenes, and the penicillium and aspergillus fungi and specifically Penicillium expansum and Aspergillus niger.
As earlier explained slime formations do in fact adhere very firmly to the structures of cooling water equipment, and in particular the slats which are for the most part produced from wood. These deposits accordingly impede the flow of the water, and often times uncontrolled detachment of the slime formations cause plugging which results in lost production and, many times, shut down of the equipment for cleaning.
In an attempt to overcome these problems, it was the present inventor's feeling that if the slime growths could be detached or sloughed off the structures at a controlled rate, the slime formations could be controlled with respect to size. By keeping the slime colonies within reasonable sizes, their fluidity within the system could be ensured.